Heretofore, in traveling-wave tubes and klystron microwave electron tubes, Pierce type electron guns have been used. Also, use of such Pierce type electron guns has been proposed in electron-beam reduction-projection (microlithography) devices (Japanese laid-open patent document no. 5-190430).
Since the Pierce type electron gun was built for use in a microwave electron tube as described above, gun performance is frequently expressed in terms of beam diameter, current density, or perveance, rather than emittance or brightness.